Did you know DNA influences your risk of diabetes?
Breaking the cycle: Genetics, type 2 diabetes and mitigating your risk
Time: around 6 BCE. Location: India. A physician places another open plastic cup filled with urine on the crowded windowsill. He looks at the trail of black ants creeping up the wall, and makes note of the samples literally covered with ants. This an early test for diabetes. Crude yet effective.
Diabetes, one of the first diseases to be described in history, now claims its fame as one of the fastest growing diseases. In 2011, 366 million people around the world were affected by diabetes, along with an estimated 180 million undiagnosed cases. Many of the factors that put us at risk for diabetes, such as obesity, lack of exercise and smoking, can be remedied. However, there is one that is out of our control. Genetic predisposition, the risk of diabetes that is passed from parents to their children in their genes.
Diabetes is a condition that affects how the body processes sugar (glucose). Glucose is the main source of fuel used in our bodies. Blood glucose levels are controlled by a hormone called insulin. When the levels are high, (e.g. after a meal), insulin is produced in beta cells of the pancreas and signals for glucose to be stored. If this circuit malfunctions and blood glucose remains high, it leads to diabetes.
There are two main types of diabetes, with the not so imaginative names type 1 and type 2. Type 1 diabetes is when the body is unable to make insulin due to their own immune system attacking their beta cells. People with type 2 diabetes can make insulin, but their bodies don’t respond to it. As their blood glucose remains high, the pancreas tries to compensate by making extra insulin. Eventually the beta cells stop functioning because they are overworked and insulin is no longer produced. Thirst, frequent urination, skin discolouration, blurred vision, slow-healing wounds and fatigue are some of the symptoms associated with type 2 diabetes.
Type 2 diabetes is a complex disease, fuelled by a combination of factors such as age, sex, obesity, physical activity and diet. However, it is also a disease with a strong genetic influence. Many studies have shown having an immediate family member with the disease, significantly increases the risk of diabetes. There’s a 40% chance of developing type 2 diabetes, if one of your parents has it. The risk increases to 70% if both parents are affected. This is why scientists have focused on genetic variations as a way to identify people that are at high risk of type 2 diabetes. These studies compare the DNA of affected individuals to the DNA of healthy individuals, searching for variants known as single nucleotide polymorphism (SNPs). SNPs are changes in the nucleotides, the building blocks of DNA.
More than 60 SNPs are already implicated in type 2 diabetes, and the list keeps growing. Many of the risk variants affect beta cell function and insulin function. The TCF7L2 gene is the gene most strongly linked to type 2 diabetes susceptibility. TCF7L2 encodes a protein known as a transcription factor that controls the levels of other genes. People with the rs7903146 risk variant of TCF7L2 produce lower levels of insulin and are at higher risk for type 2 diabetes. Other risk variants are found in the GCK gene that acts as a glucose sensor, IRS1 gene involved in relaying insulin signalling and the MTNR1B gene, which affects insulin release. However, while variants may increase the risk, not everyone who inherits them will actually develop diabetes.
Obesity has now become a public health crisis. As obesity and diabetes go hand in hand, identifying people who are at high risk for diabetes is of even more importance. Risk prediction based on genetics may prove to be a critical turning point to this problem. There is no cure for diabetes, but the risk can be mitigated through diet and exercise. With genetic knowledge, comes the power to adapt. Will it be enough motivation to break the cycle and to stop you from becoming another statistic?